It has been shown that two precursors of the aglycone of cycasin (dimethyl hydrazine and azoxymethane) are carcinogenic in germfree as well as in non-germfree rats. The locations of the tumors observed with these two compounds differ from those produced by the aglycone itself, indicating that the two compounds themselves may be active, or can be converted to active compounds other than the aglycone by the animal tissue enzymes. It has been observed that maintenance of normal levels of plasma vitamin A, in addition to being dependent upon adequate amounts of zinc, is also related to growth of the animal and/or dietary intake. It was further observed that lack of growth also resulted in below normal levels of plasma zinc. It has been possible to maintain normal levels of plasma zinc in the absence of growth by intraperitoneal administration of rather large daily doses of zinc. Preliminary results indicate that the plasma vitamin A may be increased even in the absence of growth when the plasma zinc is thus maintained.